1. Technical Field
This invention relates generally to a microwave cavity and, more particularly, to a broad bandwidth cavity that is thermally compensated.
2. Discussion
Microwave cavities have been thermally compensated as generally disclosed in U.S. Pat. No. 3,665,341 issued to Sekine et al., May 23, 1972, which is incorporated herein by reference. Generally, when the temperature of these types of devices is changed, the impedance of an oscillator within the device changes. Changes in oscillator impedance cause the frequency of the microwave signal emanating from the microwave cavity to distort. One solution to such signal variation is to combine reflected microwaves with the signal to compensate the signal distortion. Accordingly, the oscillator emits microwaves within the microwave cavity both toward and away from a waveguide coupled to the cavity. The microwaves traveling away from the waveguide are reflected to combine with and compensate the microwaves already traveling toward the waveguide. This combination of microwaves forms a compensated signal that enters the waveguide.
To properly compensate the distorted frequency of the signal, reflected microwaves must have the correct phase shift. This phase shift is determined by the distance between the oscillator and the reflective member. Thus, the distance between the reflective member and the oscillator must always be such that the reflected microwaves properly compensate for frequency distortions due to specific changes in oscillator temperature. Accordingly, an expanding and contracting member having a certain thermal expansion co-efficient is utilized. The expansion co-efficient is selected to provide precise displacement of the reflective member over a range of operating temperatures. This precise displacement ensures that the proper phase shift of the reflected microwaves is achieved to properly compensate the signal over the range of operating temperatures.
These types of temperature compensated cavities have been generally adequate for compensating high Q, relatively narrow bandwidth oscillators. However, high Q, relatively narrow bandwidth oscillators generally do not permit a high rate data link. In particular, these types of thermally compensated systems will not provide a radar system with fine range resolution. Accordingly, it would be desirable to provide a thermally compensated device for a low Q, relatively broad bandwidth oscillator.
In order to properly compensate a low Q relatively broad bandwidth oscillator, the displacement of the expanding and contracting reflective member must be generally greater than the displacement of relatively narrow bandwidth, high Q microwave cavities described above. Accordingly, it would be desirable to provide an expanding and contracting reflective member that is compact in size and capable of providing generally greater displacement of a reflective member.